i Hydrogeological Assessment of Whitemoss Landfill on behalf of ARROW by: Author: Hannah Fraser, H Fraser Consulting Ltd. Reference 30047R1v1Whitemoss Registration number: 10024954 Case number: WS010003 Date: July 2014 Summary 1 Statement 6 1 AUTHOR BIOGRAPHY 6 1.2 Education and professional qualifications ............................................................ 6 1.3 Summary of professional career........................................................................... 7 1.4 Selected project experience ................................................................................. 7 2 INSTRUCTIONS 11 2.2 Objectives ........................................................................................................... 12 2.3 Scope of works ................................................................................................... 13 Contents
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i
Hydrogeological Assessment of Whitemoss Landfill on
behalf of ARROW by:
Author: Hannah Fraser, H Fraser Consulting Ltd.
Reference 30047R1v1Whitemoss
Registration number: 10024954
Case number: WS010003
Date: July 2014
Summary 1
Statement 6
1 AUTHOR BIOGRAPHY 6
1.2 Education and professional qualifications ............................................................ 6
1.3 Summary of professional career ........................................................................... 7
lagoon and treatment plant, landfill gas flare and interceptor waste treatment facility.
4.3.2 Early operations at the site comprised peat and clay excavation; the site has
a history of waste management activities since the 1970s, and in 1991 was subject
to waste management licence no 354, which permitted landfill only of inert wastes.1
The mechanism by which the site input was varied to include special wastes is
ambiguous. The 2013 HRA review says: From information presented in the
Regulation 15 Report dated January 1997 (reference 4) the Waste Management
Licence permitted the landfilling of "a variety of wastes including special wastes".
4.3.3 The current landfill comprises Cell1 and Cell2 (now restored) and Cell3
which is operational. The landfill void was excavated to approximately 44 m OD, (i.e.
below the water table), and a groundwater drainage system (GDS) comprising a
sump and drainage network installed (see Figure ES21C). A mineral liner comprising
a 1 m thickness of site won clay and a synthetic liner were placed in the void, and
waste was placed. The permit allows for discharge of 235 m3/d of groundwater to a
drain on the eastern boundary of the site, however in practice groundwater discharge
is used for dust suppression and the remainder discharges via the leachate lagoon
1 The ESID says at § 1.7 “Landfilling with inert waste was the subject of a Waste Management
Licence (number 354) issued on 4 October 1991. In June 2003 an application was made for a Pollution Permit Control (PPC) Permit for the operation of a hazardous waste landfill at the site”. The mechanism by which the site input was varied to include special wastes is ambiguous. The 2013 HRA review says only: “From information presented in the Regulation 15 Report dated January 1997 the Waste Management Licence permitted the landfilling of "a variety of wastes including special wastes"
Hannah Fraser
30047R1v1 26
and treatment plant. Leachate is pumped from leachate extraction sumps in each of
the landfill cells to the leachate lagoon and treatment plant, from where it is
discharged to sewer.
4.3.4 The landfill operates under the principle of hydraulic containment; whilst the
void is being filled the water table is controlled below the level of the landfill.
However, once sufficient waste is present to balance hydrostatic forces, groundwater
levels are allowed to rise around the landfill void. Leachate levels are maintained at
the base of the landfill void so that groundwater levels are always higher than the
leachate levels and groundwater flow will be into the landfill void (at a rate limited by
the low permeability of the liner system), in theory preventing escape of leachate
from the landfill void and pollution of groundwater.
4.3.5 The interceptor waste treatment facility processes waste from drainage
interceptors, for example from fuel station forecourts, by a process of separation and
filtration. The process creates a liquid discharge and a filtration residue which is
landfilled. The residue is likely to include petroleum hydrocarbons and polycyclic
aromatic hydrocarbons.
4.3.6 The current permit allows for disposal of hazardous wastes that could
include a very wide range of hazardous substances with a high potential to pollute
the environment. Some waste streams are reasonably predictable in their chemical
signature, but others such as waste soils from contaminated sites might contain a
wide range of unpredictable and exotic chemicals. The permit also allows for the
disposal of biodegradable material such as wood and textiles, which have the
capacity to generate significant quantities of landfill gas.
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30047R1v1 27
Environmental Compliance
4.3.7 Table 4.1 presents the monitoring requirements for the current operation;
monitoring submissions to the Environment Agency since 2010 have been provided
by WLL, and are commented on in the table.
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Table 4.1 Environmental monitoring requirements
Schedule Description Comment
S4.1 Weekly monitoring of leachate levels above the landfill cell base
Data indicate compliance with the limit of 1 m above the base of the landfill.
S4.3 Weekly monitoring groundwater drainage water (i.e. from the sub-landfill dewatering) of suspended solids, pH, ammoniacal nitrogen, oil or grease, flow, volume, and any List 1 substances found in the annual leachate screening.
Reports state that underground water is being discharged to the leachate lagoon and used for dust suppression. Flow rates and quality data are therefore not available. Limits on discharge to the watercourse include a volumetric limit of 235 m3/d and a limit on the concentration of ammoniacal nitrogen of 2.5 mg/l.
S4.4 Continuous monitoring of flows and monthly monitoring of cadmium and mercury concentrations in discharge of leachate to sewer
Discharge to sewer is generally close to the limit of 50 m3/d for 5 days per week (no pumping at weekends). N.b. the permit states a limit of 50 m3/d, but the reports state a limit of 150 m3/d. Data for cadmium and mercury concentrations are absent in Q3 and Q4 of 2012.
S4.5,
S4.11
Quarterly monitoring of groundwater from 11 boreholes and the underdrainage effluent for cadmium, mercury, benzene, toluene, xylene, ammoniacal nitrogen, chloride, arsenic, nickel, phenol.
Monitoring of groundwater at 11 boreholes and underdrainage effluent: monthly for water level, conductivity, pH, ammoniacal nitrogen, chloride, COD; quarterly for sulphate, ammoniacal nitrogen, phenols, arsenic, TON, Na, K, Ca, Mg, Cr, Cd, Mn, Fe, Cu, Ni, Zn, Pb, Hg, Cyanides, benzene, toluene, xylene, List 1 screen. l
Conductivities are often of the order of 1000 – 3000 uS/cm. Manganese concentrations are high, sometimes up to c. 2000 ug/l., Ammoniacal nitrogen concentrations are up to 7.2 mg/l, often around 2 or 3 mg/l in certain boreholes.
S4.9 Monitoring of leachate in each cell collection sump: weekly for conductivity, temperature, pH; quarterly for
Conductivities are regularly of the order of 20,000 – 50,000 uS/cm. Chloride, and manganese concentrations are frequently of the order of
Hannah Fraser
30047R1v1 29
Schedule Description Comment
ammoniacal nitrogen, chloride, sulphate, alkalinity, phenols, COD, BOD, TOC, TON, Na, As, K, Ca, Mg, Cr, Cd, Mn, Fe, Cu, Ni, Zn, Pb; Annually for mercury, toluene, xylene, benzene and a list 1 screen.
20,000 mg/l and 1,500 ug/l, compared with assessment limits of 4534 mg/l and 42 ug/l. Ammoniacal nitrogen concentrations are frequently of the order of 1000 mg/l.
Toleune concentrations in 2013 were 83 ug/l, approaching the limit of 84 ug/l. Also in 2013, Aldrin R concentrations were the same as the assessment limit of 0.1 ug/l.
S4.10 Monitoring of surface water at two streams; weekly for conductivity, pH, total suspended solids, visible oil and grease, ammoniacal nitrogen; quarterly for chloride, sulphate, alkalinity, phenols, COD, TON, Na, K, Ca, Mg, Cr, Cd, Mn, Fe, Cu, Ni, Zn, Pb, Hg, List 1 screening.
Reports state that the streams were ‘dry, stagnant, water not representative’ or ‘unable to sample still water’ or ‘’stagnant water in both streams, sample not representative’.
(n.b. the 2010 quarterly reports for Q2 and Q3 include chlorobenzene, pentachlorophenol, and trifluralin in the list of determinands that were detected in Annual Leachate screening and are to be included in quarterly monitoring, although nothing is reported as samples were not taken)
Hannah Fraser
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HRA Review
4.3.8 A four-yearly HRA review is required to provide an assessment of trends in
groundwater quality and a comparison of groundwater quality against trigger levels.
Letters from the Environment Agency detail late submission of the most recent HRA
review, which was eventually submitted in March 2013, and has not yet been Duly
Made. The Environment Agency’s letter in response to the report submission is
presented in Appendix A. The EA draw attention to uncertainty in the conceptual
model for the site, stipulate a requirement to assess a wider range of contaminants
than was addressed in the HRA review, and note that hydrographs show
groundwater elevations to be rising and the requirement to make an estimate of
future recovered groundwater elevations.
4.3.9 Surface water quality
4.3.10 The ES reports that surface water monitoring was undertaken on 22
occasions between 2006 and 2009. Average concentrations of cadmium,
ammoniacal nitrogen, chromium, iron, manganese and lead exceeded
Environmental Quality Standards. Additionally, maximum concentrations of mercury,
nickel, zinc and sulphate exceeded Environmental Quality Standards (EQS).
4.3.11 The ES states that the concentrations are considered to represent
groundwater quality in the Coal Measures, but does not explain how water from the
coal measures is present in the ditches, which are significantly elevated above the
Coal Measures and separated by Glacial Till. The ditch to the east of the site may
have been subject to discharge from groundwater drainage system, in which case
the landfill operation may have been discharging List 1 substances (cadmium and
Hannah Fraser
30047R1v1 31
mercury) to a water course. It is not clear how water from the coal measures would
get into the ditch to the west of the site, as there is a thickness of till between the
surface water and the deep groundwater system.
Groundwater quality – shallow groundwater
4.3.12 The ES presents groundwater quality data from two sampling rounds in May
2013 and June 2013. The data are from the 5 shallow E series boreholes. All
boreholes showed elevated concentrations of ammoniacal nitrogen, chromium and
manganese. This may suggest a naturally occurring chemically reducing
environment, or may be as a result of anthropogenic sources. It is considered that
the data set does little to characterise the background quality of the groundwater in
the shallow system, as data are not available from the existing landfill site for
comparison. In addition, background concentrations of key contaminants including
polycyclic aromatic hydrocarbons and petroleum hydrocarbons have not been
assessed.
Groundwater quality –groundwater in the Coal Measures
4.3.13 Groundwater quality monitoring data show exceedences of the EQS for
arsenic, ammoniacal nitrogen, iron, manganese, nickel, phenols and sulphate. High
conductivities are associated with high sulphate concentrations. Iron, manganese,
sulphate and ammoniacal nitrogen may be associated with the Coal Measures but it
is not clear where arsenic, nickel or phenols derive from.
4.3.14 The provision of data in the format of minimum, maximum and mean does
not allow an assessment of trends or seasonal variations, and does not allow for
proper spatial assessment.
Hannah Fraser
30047R1v1 32
4.3.15 The groundwater quality data does not include a full suite of hydrocarbons,
including priority pollutants such as polycyclic aromatic hydrocarbons or VOCs, and
it is not clear from the available data that annual screening would have picked up
these organic or other exotic compounds. It is noted that it is not a requirement of the
current landfill permit to monitor these substances in groundwater, but it is
considered that the background chemical status of the aquifer cannot be properly
assessed if these data are not acquired.
Groundwater control
4.3.16 The current operations are understood to have included pumping of
approximately 450 m3/d from the groundwater sump, to maintain groundwater levels
below the base of the void. The elevation of the sump is approximately 44 m OD. It is
noted that volumetric data are not available, and that where this volume is reported,
it is based on communications with WLL personnel rather than examination of
monitoring data. The stated volume of groundwater pumping to achieve a dewatered
void space is not supported by objective evidence.
4.3.17 Anecdotal accounts from local residents report that there has been some
difficulty at the site with basal heave, due to hydrostatic pressures from groundwater.
This has not been substantiated, but is considered possible or even probable, given
the high piezometric elevations in the Coal Measures. Basal heave might result in
significant movement of the floor of the void and damage to the clay and HDPE
liners, to the extent that the long term containment of the facility is compromised.
Hannah Fraser
30047R1v1 33
4.4 Proposed operations
4.4.1 It is proposed to excavate the superficial materials and stockpile them. The
proposed landfill will be operated in four phases, (A, B, C, D), with each phase
incorporating excavation of the coal measures, placement of a groundwater drainage
system, placement of 1 m of clay with an 2 mm thick HDPE synthetic liner. The
formation depth is approximately 50 m OD (Figure ES20). Groundwater control will
be maintained to keep the water table below the base of the void whilst waste is
placed. When the waste is deep enough to counter the upward hydrostatic pressure
of groundwater, the groundwater system will be turned off, and leachate levels
controlled at 1 m above the base of the landfill.
4.4.2 The settled restoration levels for the site are below 77 m OD, with slopes
from two central plateaus down to elevations of c. 66 m OD on the northern and
western boundaries (Figure ES5)
4.4.3 The void will be dewatered and a groundwater drainage system will be
installed in the base and sides of the void as necessary. Groundwater will drain to a
sump from where groundwater will be pumped to the surface water management
system. A leachate collection system will be installed across the base of the landfill.
Leachate extraction wells will be installed in the landfill to facilitate the removal of
excess leachate and to control leachate levels. Following completion of filling the
landfill will be capped with a 1m thick clay cap covered with a geocomposite
drainage layer underlying restoration materials.
Hannah Fraser
30047R1v1 34
Environmental Permitting
4.4.4 It is understood that an Environmental Permit application has been made to
the Environment Agency to vary the existing permit to extend the existing permitted
site and authorise the disposal of hazardous waste in the western landfill area.
4.4.5 The Environment Agency confirm that this application has not been duly
made, i.e. it does not contain the required components and sufficient information for
it to begin to be determined (EA, 2010a). There is therefore no indication as to
whether the Environment Agency will grant an environmental permit for the proposed
landfill.
Water management plans
4.4.6 Surface water management plans have been prepared by Wardell
Armstrong (2013), presented as Appendix ESD of the Environmental Statement. The
proposed water management system comprises ditches at the base of all landfill
slopes around the perimeter of the site. These discharge via 4 discharge points, with
the discharge rate restricted to the greenfield run-off rate of 58 l/s. Storage in the
form of lagoons and ditches is provided for each discharge point, to allow high flows
to be attenuated during high rainfall events. The total storage in the system is
10,110 m3. Pumped groundwater will also be discharged to this system, having first
been passed through a filtering system to remove suspended solids.
4.4.7 Whilst run-off and surface water discharge rates have been roughly
quantified, no attempt has been made to quantify the groundwater discharge.
Hannah Fraser
30047R1v1 35
Dewatering the peat
4.4.8 The impact of the proposed operation on groundwater levels in the Peat and
Shirdley Hill Formation, or related water features, has not been considered.
Dewatering the coal measures
4.4.9 It has been assumed in the HRA that the Coal Measures can be dewatered,
and that groundwater inflow volumes will be 400 m3/d (4.6 l/s), based on an estimate
of the discharge rate provided by Whitemoss Landfill Ltd. Appendix 5 of the revised
HRA presents calculations of the discharge from the groundwater drainage system,
which ranged between 161.7 m3/d and 2088.2 m3/d, or between 1.8 and 24 l/s.
4.4.10 The impact of dewatering on surrounding groundwater elevations has not
been explicitly discussed, however it is evident from hydrographs (Appendix ESY)
and groundwater contours (Figure ES21C) that pumping from the groundwater sump
at an elevation of 44 m OD induced a drawdown of approximately 6 m OD at the
furthest monitoring point (BH E50), approximately 500 m distant. The zone of
influence of pumping would appear to be elongated on a northwest-southeast strike,
although the influence to the southeast has not been observed due to lack of
monitoring, (i.e. off-site monitoring boreholes). It is noted that the water features to
the southwest of the site, are between 675 m and 1100 m from the site.
4.4.11 It is considered that the assessment of the impacts of dewatering on local
water features is inadequate.
Hydrogeological Risk Assessment
4.4.12 The predicted impact of the proposed and current landfills has been
assessed in the Hydrogeological Risk Assessment (MJCA, 2014). The future landfill
Hannah Fraser
30047R1v1 36
operation is considered in three stages: the early operational stage, when the landfill
void is being filled and groundwater and leachate levels are controlled; the late and
post-operational stage when groundwater levels are allowed to rebound, but
leachate levels are controlled to within 1 m of the base of the landfill (this means that
groundwater that flows into the filled void space is pumped out as leachate); and the
late post operational stage, when it is deemed that leachate concentrations are low
and leachate levels can be allowed to equilibrate with groundwater levels.
4.4.13 The operational phase of the landfill has been assessed using a Landsim
model; the late and post operational phase has been assessed using the
Environment Agency’s spreadsheet tool for hydraulic containment; and the late post-
operational phase has not been assessed (it is assumed that leachate
concentrations are benign at this phase). Note that this is in contravention to the
Environment Agency’s request that risk assessment at the site needs to consider
when the wastes become sub-water table (Appendix A).
4.4.14 The HRA defines a leachate source term by which to model potential future
impacts, including arsenic, benzene, cadmium, ammoniacal nitrogen, chloride,
phenols, and zinc. The Environment Agency’s letter of May 2013 stipulates that
modelling for the proposal site needs to cover ‘all appropriate hazardous and non-
hazardous substances’. It is considered that the range of contaminants modelled is
very restricted and does not adequately characterise risks to the environment.
Hannah Fraser
30047R1v1 37
5 TECHNICAL ASSESSMENT
5.1.1 This section of the report presents the technical calculations and arguments
used and developed to meet the report objectives.
5.2 Baseline Characterisation
5.2.1 The conceptual hydrogeological model put forward in the ES is not
considered sufficiently robust to characterise the baseline setting. The period of
groundwater level monitoring does not cover a full hydrogeological cycle, hence
winter (high) groundwater levels are unknown, and no attempt has been made to
relate observed groundwater levels with rainfall events or other hydraulic stresses
which would enable an informed understanding of the hydrogeological regime. Much
of the historic groundwater level data has been identified as unreliable, as borehole
construction did not allow differentiation between the shallow and deep aquifer
systems, and in any case groundwater levels were affected by dewatering activities.
5.2.2 It is noted that many of the borehole logs for the proposal site rely on drillers
descriptions of strata and are not compliant with British Standard BS
5930:1999+A2:2010 ‘Code of practice for site investigations’. Much useful
information relating to water inflows in all strata including the Glacial Till, and
fracturing in the Coal Measures has not been recorded.
5.2.3 The hydrogeological setting is highly complex, comprising a dual aquifer
system, with high degree of anthropogenic modification through Coal Mining and
Peat extraction activities. The siting of a hazardous waste facility in this setting
without adequate hydrogeological characterisation is considered to present an
unacceptable risk to identified and unidentified water features. The lack of a holistic
Hannah Fraser
30047R1v1 38
conceptual understanding has led to a number of deficiencies in the technical
assessment of risks and impacts. Of particular concern are:
• The impacts of dewatering the shallow system have not been addressed.
• The impacts of dewatering the Coal Measures aquifer have not been
quantified, and the volumes of underdrainage water required to be managed
via the surface water management system have not be adequately quantified.
• The presence of many water features and a groundwater discharge zone to
the south of the site is not identified in the ES or HRA, and baseline
characterisation and impact assessment for these features has not been
carried out.
• The proposals for monitoring and surveillance (and the baseline water quality
data sets) do not include key organic pollutants that will be present in the wide
range of wastes authorised by the permit.
• The proposals for management and monitoring of the late post operational
phase of the landfill are considered inadequate.
• There has been insufficient consideration of the likely problems of basal
heave associated with this specific hydrogeological setting.
5.3 Dewatering the shallow system
5.3.1 Dewatering of the sands/peat has not been taken into consideration in the
ES. These materials will be excavated across much of the proposal area, leaving an
excavation face around the perimeter of the void.
Hannah Fraser
30047R1v1 39
5.3.2 Appendix B presents calculations of the likely inflow to the void as a result of
dewatering the peat, and estimates of the radius of influence of dewatering. Inflows
are estimated at between 200 m3/d and 400 m3/d. The water management plan has
not accounted for these inflows. In order to provide hydraulic containment, these
strata must be lined, however seepage on these faces is likely to contribute to
instability in the landfill liners, particularly as it may take some years for the void to fill
and for waste materials to be placed against these slopes.
5.3.3 Warburton et al. (2004) defined peat as a biogenic deposit which when
saturated consists of about 90-95% water and about 5-10% solid material. According
to Warburton et al. (2004) further, the organic content of the solid fraction is very
high, often up to 95% and is made up of the partly decayed remains of vegetation
which has accumulated in waterlogged areas over timescales of 102-103 years. This
renders peat as an extremely soft organic soil with very low bearing capacity and
high compressibility.
5.3.4 The radius of influence of dewatering the superficial aquifer is estimated at
between 20 m and 90 m (Appendix B). It is highly likely that dewatering of the Peat
will cause subsidence on the northern boundary of the site. Dewatering of the peat
may extend up to 90 m from the boundary of the excavations, and the strength of the
peat will be compromised even further as the water content is diminished. The
integrity of the road is likely to be compromised, and there is the possibility of
structural damage to the properties on the northern boundary, and to drainage
infrastructure. No account has been taken of this in the Environmental Statement.
Hannah Fraser
30047R1v1 40
5.4 Dewatering the Coal Measures
5.4.1 Dewatering of the proposed facility will lower the water table at the proposal
site to less than 50 m OD, lower if the excavations have to progress deeper to win
coal which has been proved to depths of 40 m OD. This will create a zone of
depressed groundwater levels, with an influence that might be far reaching. The ES
estimates groundwater inflows to the GDS to be of the order of 400 m3/d, based on
anecdotal evidence of historic pumping rates from WLL.
5.4.2 The Minor Aquifer Properties Manual (Jones et. al. , 2000) reports that ‘ In
the Wigan area, yields from boreholes up to 300 mm diameter generally range from
432 m3/d to 864 m3/d, while large diameter mine shafts occasionally yield up to
1680 m3/d. …Much higher yields are observed from boreholes penetrating flooded
disused workings’.
5.4.3 Calculations of groundwater inflow to the GDS have been made and are
presented in Appendix B. A reasonable range for an estimate of pumping from the
GDS is considered to be 3000 m3/d – 17000 m3/d, or 34 – 190 l/s. The lower end of
this range assumes a larger radius of influence, as observed from recent pumping at
the site, and the higher end of the range assumes a higher hydraulic conductivity,
consistent with a highly fractured aquifer.
5.4.4 Appendix ESD describes the surface water management plans for the site,
which comprise a network of drainage channels around the site perimeter which feed
four storage lagoons, which in turn discharge to the local surface water drainage
system via culverts. The greenfield run-off rate for the site is 58 l/s. This is the rate
at which discharge to surface water drains should be restricted in order not to cause
Hannah Fraser
30047R1v1 41
inundation downstream of the site. The total storage capacity in the surface water
lagoons is 10,110 m3.
5.4.5 At the GDS discharge rates described, groundwater pumping alone is highly
likely to exceed greenfield run-off rates. At the lowest estimated pumping rates, it
would take approximately 3.5 days to fill the surface water storage system, after
which there would be no capacity for storage of incident rainfall. There would be
regular exceedences of greenfield run-off rates in response to rainfall, or flooding at
the site. At the higher end of the range of estimated pumping rates, the entire system
would be inundated within a day, resulting in either on site flooding or off-site
discharge at rates far exceeding the greenfield run-off rate.
5.4.6 As discussed above, the quality of the Coal Measures groundwater is poor,
with concentrations of arsenic, ammoniacal nitrogen, iron, manganese, nickel,
phenols and sulphate exceeding EQS. Discharge of untreated groundwater to the
surface water drainage system will be in contravention of the Landfill Directive (1999)
and Water Framework Directive (2010) due to the presence of hazardous
substances and non hazardous pollutants. The ES states that groundwater will
undergo filtration prior to discharge, but this will not provide treatment of the
identified substances, and the infrastructure proposed will not be sufficient to
process the volumes anticipated.
Use of groundwater discharge for dust suppression
Current site practice is to use groundwater discharge for dust suppression.
Groundwater monitoring around the proposal site shows the groundwater to include
concentrations of both hazardous substances and non-hazardous pollutants; use of
Hannah Fraser
30047R1v1 42
this water for dust suppression will therefore constitute a discharge of hazardous
substances and non-hazardous pollutants to the Peat and Shirdley Hill Sands
aquifer, in contravention of the Water Framework Directive (2010). Whilst a
proportion of dust suppression water will evaporate, and some be drawn back into
the landfill void via shallow groundwater flow, some may discharge to the surface
water drainage system and ultimately the River Tawd.
5.5 Water features survey
5.5.1 To comply with the Schedule 4 of the Town and Country Planning
(Environmental Impact Assessment) Regulations 2011 (“the EIA Regulations”), and
with the Water Act (2003) (which requires a Hydrogeological Impact Assessment to
accompany an application for a licence to dewater mineral excavations), it is usual
for sub-water table mineral extraction planning applications to include a water
features survey, which identifies all local water features, attempts to understand how
they are connected with the hydrogeological regime, and provides sufficient baseline
monitoring and technical assessment to provide a quantitative assessment of how
dewatering will affect flow and quality of the identified features. The survey will
include fieldwork, to make sure that all private boreholes, water abstractions,
streams, springs and ponds are identified, rather than relying on map-based reports
and national databases. This level of work has not been undertaken as part of the
ES, and it is considered that the failure to properly consider the water features in the
Coal Measures groundwater discharge zone to the south of the site presents a
significant risk to these receptors.
Hannah Fraser
30047R1v1 43
5.6 Review of HRA and predictions for groundwater quality
5.6.1 The models used to predict impacts to groundwater quality assume
groundwater flow in a porous media. It is clear from borehole logs and responses to
groundwater pumping that the Coal Measures aquifer is highly anthropogenically
modified, and that flow is both enhanced and restricted on linear features such as
fractures and mine workings, with links between features created by fracture zones
and subsidence zones. The models used are not appropriate to predict contaminant
transport in this setting.
5.6.2 Regulatory guidance on hydrogeological risk assessment for landfill is given
in the Environment Agency’s Horizontal guidance Note H1 Annex J 3. Additional
guidance for hydrogeological risk assessments for landfills and the derivation of
groundwater control levels and compliance limits.
5.6.3 It is considered that the suite of source chemicals modelled in the HRA is too
limited to properly assess potential impacts to receptors. In particular, the impact of
hydrocarbons is limited to benzene. The landfill has a steady waste stream from the
interceptor waste plant, which is derived from oil and fuel, and the impact of
polycyclic aromatic hydrocarbons such as naphthalene (considered relatively mobile)
and benzo(b/k)anthracene, benzo(ghi)perylene and indeno(123-cd)Pyrene (which
have extremely low EQS and are Priority Substances under the Water Framework
Directive, 2010) should be assessed, as these compounds will be present in the
waste stream. Other weaknesses in the assessment include selection of hazardous
substances and non hazardous pollutants that have relatively high Environmental
Quality Standards. For example, the EQS for zinc ranges from 8 ug/l to 125 ug/l
(depending on water hardness), compared with an EQS for copper of between 1 ug/l
Hannah Fraser
30047R1v1 44
and 28 ug/l. Zinc has been assessed rather than copper. Cadmium, which has an
EQS ranging from 0.08 ug/l to 0.25 ug/l has been assessed rather than mercury
which has an EQS of 0.05 ug/l.
5.7 Late post operational impacts
5.7.1 The proposal is to maintain leachate levels within 1 m of the base of the
landfill in the later operational and early closure phase, until leachate concentrations
are considered benign. Leachate control will then be removed, and leachate levels
allowed to rise. The waste mass will be capped at this point, and flow into the landfill
will be derived by slow inflows through the landfill liner and cap. Leachate levels
within the landfill will rise to eventually equilibrate with groundwater elevations.
5.7.2 This process is considered highly likely to create a leachate body with a
highly polluting potential. The landfill mass will have been capped for several years
as the leachate levels were controlled, and will essentially be dry. As groundwater
levels re-equilibrate, groundwater will flow into the landfill, (at low rates if the liner is
not compromised), the waste mass will (slowly) become saturated and the chemical
environment will change significantly. The redox environment will change, and
degradation of compounds and substances by chemical and biological reactions will
take place, with the potential release into the aqueous phase of hazardous
substances and no-hazardous pollutants that were stable within the unsaturated
waste mass. At this stage in the process, all leachate and groundwater management
operations will have ceased, hydraulic containment will have been switched off, and
the leachate will migrate through the liners, and through tears and holes in the liners,
with the flow of groundwater. It is considered inadequate for the HRA to have not
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considered management of groundwater and leachate rebound rates, and monitoring
of leachate and groundwater quality into the late-post operational phase.
5.8 Requisite Monitoring and surveillance
5.8.1 The HRA presents recommendations for monitoring of leachate,
groundwater and surface waters during the operational and early post operational
phases of the landfill. Determinands to be monitored comprise arsenic, benzene,
cadmium, ammoniacal nitrogen, chloride, phenols and zinc (with additional
monitoring of suspended solids, pH, oil or grease and flow in surface waters).
5.8.2 The suite of chemicals proposed for monitoring is considered highly
restricted, a significant reduction over existing monitoring programmes, and
inappropriate given the wide range of waste types that may be landfilled under the
current permit (it is noted in particular that there are no proposals to monitor lead,
despite the landfilling of CRT glass at the current site, which has high lead
concentrations). The restricted list of quality data will preclude hydrochemical
assessment of the groundwater regime, which will be required if pollution is
suspected. The proposals do not include for annual screening of leachates to identify
possible additional pollutants, as recommended by Horizontal guidance Note H1
Annex J 3. This guidance requires that the following screening tests are undertaken
to assess leachate on an annual basis.
i) GCMS scan for volatiles;
ii) GCMS scan for semi-volatiles;
iii) derivitised GCMS scan for semi-volatiles;
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iv) extraction of organotin compounds;
v) reduction of mercury compounds; and
vi) solution of cadmium compounds.
5.8.3 The proposals for monitoring of surface waters include derivation of control
levels and compliance targets based on average future water quality. This is
because recent data from stream samples are not available. This proposal could
result in future control levels and compliance targets being based on the average
concentrations of polluted site discharges, and this approach is considered highly
flawed. It would be more appropriate to adopt standards based on historic water
quality data.
5.8.4 The monitoring proposals do not include for monitoring of the volume of
discharge from the groundwater drainage system. This parameter is important in
demonstrating whether or not groundwater control is taking place, and in
understanding the responses of the system to hydraulic stresses. It is also a
requirement for dewatering activities to record abstraction volumes (Water Act,
2003).
5.8.5 Environmental Assessment levels are based on mean groundwater
concentrations in the Coal Measures, from boreholes around the existing and
proposed landfills. This is considered inappropriate, as the groundwater quality may
be impacted by the existing landfill.
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5.9 Basal Heave
5.9.1 Due to the high elevation of groundwater in the Coal Measures (c. 64 m OD
measured from March – June 2013, conservatively estimated as 66 m OD in winter
months), there will be considerable upwards hydrostatic pressure on the basal liner
once groundwater control measures cease. If this pressure is not countered by a
sufficient thickness of waste of an appropriate density, the integrity of the basal liner
will be compromised, allowing groundwater/leachate movement between waste
mass and the Coal Measures aquifer.
5.9.2 Appendix C presents scoping calculations to assess the thickness of waste
required to balance the hydrostatic forces at the base of the landfill liner. Assuming
the formation level is at 50 m OD, 23.3 m of material will be required above the base
of the landfill, resulting in a finished height of 73.3 m OD. Under winter groundwater
elevations (assumed to be 66 m OD), 26.7 m of waste will be required, resulting in a
finished height of 76.7 m OD.
5.9.3 If coal is encountered during the excavation (considered likely), there will be
a requirement to win the coal, and therefore excavate to greater depths. Borehole
logs show thin seams of coal ranging between 40 m OD and 52 m OD. If a formation
depth of 40 m is required to win coal, the corresponding finished height of material
above the base to counter upwards hydrostatic forces is 83.3 m OD. Should
groundwater levels rise to 69 m OD, the final height required would be 88.3 m OD.
The proposed settled restoration levels of the proposed landfill are 77 m OD on the
central plateau, with the majority of the site area lying between 76 and 68 m OD.
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5.9.4 It is clear from consideration of these simple scoping calculations that the
integrity of the basal liner may be subject to catastrophic pressures under moderate
and highly plausible conditions of groundwater rise and low waste density. It is not
clear that operational controls will be sufficiently robust to ensure that these
considerations are taken into account, and in any case, rising regional groundwater
levels will be beyond control in the post-closure phase.
5.9.5 The reader’s attention is drawn to the problem of management of the
groundwater discharge. In the event that the surface water drainage and storage
system is full, it might be normal operating practice to cease groundwater pumping
for the duration of a storm event or rainy period, until capacity in the system is
available again. However, as shown above, allowing groundwater levels to rise when
there is insufficient waste present to balance hydrostatic forces will initiate conditions
likely to instigate failure of the landfill liner.
5.9.6 The reader’s attention is also drawn to the fact that disruption of the liner
system may go unobserved as it may occur when there is a significant thickness of
waste in the landfill.
5.9.7 The longer that the landfill takes to fill, the higher the risk that an event will
occur to initiate basal heave and rupture of the liner. It is understood that fill rates for
the current landfill have been slower than anticipated, and that future fill rates may
also be uncertain.
5.9.8 There will be seepage from the superficial aquifer, and possibly from the
Glacial Till, which will also contribute to liner instability further up the liner slopes if
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the strata are not either pre-dewatered or sufficient thickness and density of material
placed on the slope to prevent heave.
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6 CONCLUSIONS
6.1.1 The conclusions of the study are presented as answers to the questions
posed in the study brief, below.
Has the hydrogeology been adequately characterised and understood in order
to allow potential impacts to be properly assessed?
6.1.2 It is clear from the available data that the structure of the Coal Measures is
complex, and that the system includes effective barriers to groundwater flow, and
high transmissivity conduits for groundwater flow. The characterisation of the system
is considered inadequate, with no attempt made to explain groundwater
hydrographs, link groundwater elevations with rainfall or other hydraulic stresses
such as pumping and recharge from drains.
6.1.3 The assessment relies heavily on permeability measurements made in 2003
on the existing site that are likely to be significantly lower than at the proposal site.
6.1.4 The baseline groundwater quality has not been adequately characterised to
allow the impacts of possible future pollution to be assessed. Organic compounds
have not been reported.
6.1.5 A water features survey has not been undertaken, and predictions of the
radius of influence of dewatering in either the superficial aquifer or the Coal
Measures aquifer have not been undertaken.
6.1.6 Impacts of dewatering the peat on local groundwater levels and resulting
subsidence issues have not been considered.
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6.1.7 In answer to the question above, the characterisation of the system is not
considered adequate to allow potential impacts to be assessed or mitigated.
How certain is it that the Coal Measures can be adequately dewatered through
the lifetime of the operation, and have the hazards associated with mining
infrastructure been properly considered?
6.1.8 Predictions of the groundwater abstraction rates required to dewater the
Coal measures made by the author are between 1 and 2 orders of magnitude higher
than those assumed by the ES, and if realised would result in either discharge to
surface water significantly in excess of greenfield run-off rates, inundation of the site,
or a failure to lower the water table to the required depth. The discharge rates
assumed in the ES are unsubstantiated estimates provided by WLL to their
consultants.
6.1.9 It is considered highly uncertain that the Coal Measures can be adequately
dewatered under the current proposals; there is not sufficient understanding of the
complexity of the mined-out Coal Measures aquifer and the flooded mine workings to
be confident of dewatering predictions and, given the highly polluting potential of the
hazardous waste facility and the abstracted groundwater, it is considered that the
environmental hazards have not been properly considered.
Have the likely quality and cost implications of treating the abstracted
groundwater been adequately considered?
6.1.10 The proposed treatment of groundwater prior to discharge to the surface
water drainage system is filtration. Filtration is considered inadequate to treat the
concentrations of hazardous substances and non-hazardous pollutants observed in
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groundwater monitoring at the proposal site. The likely volumes would require
significant infrastructure that has not been included for in the ES. There is no
evidence that the quality and cost implications of groundwater treatment have been
adequately considered.
How certain is it that hydraulic containment can be achieved?
6.1.11 It is not certain that hydraulic containment can be achieved. In the first
instance, lowering the water table sufficiently to construct the landfill may be highly
problematic in this area which is subject to intensive fracturing and mining related
subsidence. If the landfill is successfully constructed, groundwater levels will have to
be maintained at below the base of the landfill until a very significant thickness of
waste is placed, to ensure against basal heave and rupture of the clay liner. If
groundwater abstraction has to stop due to pump malfunction, or lack of capacity in
the surface water storage and drainage system, groundwater levels will rise and the
integrity of the basal liner may be compromised. If the excavation has to proceed to
greater depths than anticipated due to the obligation to win coal, the required
thickness of waste to balance hydrostatic forces will be increased; if this is not
managed the integrity of the basal liner may be compromised. Hydrostatic forces will
also be acting on the liner on the slopes of the landfill due to inflow from the
superficial aquifer (and to a lesser degree from seepages from the Glacial Till) and
this has not been considered in the ES. Uncertainty in fill rates for the landfill
exacerbate the risk of basal heave and rupture of the liner. Finally, high winter water
tables or rising groundwater levels due to climate change or changes in local
groundwater abstraction may result in higher than expected ambient groundwater
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levels, basal heave and rupture of the liner during the post operational phase of the
landfill.
How certain is it that the leachate management systems will properly deal with
groundwater rebound and leachate development once operations cease, and
that long term management plans will be adequate?
6.1.12 The ES states that ‘leachate management will continue for as long as
necessary and will not cease until the EA agree that leachate management is no
longer needed’. It is considered that this leachate management should rightly allow
for a controlled rebound of leachate levels in the waste mass, so that the
development of the saturated chemistry of landfill can be monitored. However the
HRA does not provide an assessment of this process (it rather assumes that post-
closure leachate concentrations will be benign). There is no estimate of how long it
will take for leachate levels to rebound or what the likely evolving chemistry will be,
nor is there a modelling scenario that assesses the risks arising from the saturated
waste mass. It is therefore not at all certain that appropriate long management plans
will be put in place to adequately mitigate risks of pollution; as there is a significant
possibility that the long-term management of leachate rebound and quality will be
onerous, it is considered highly inappropriate to commence operations without a
fuller assessment of these long term liabilities.
6.1.13 In addition to the questions above, the following comments are made:
• For as long as the Environmental Permit allows for disposal of biodegradable
or volatile wastes at the site, it should be a stipulation of the future operation
that landfill gas monitoring and management is undertaken.
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• The proposals are considered to be non-compliant with the following
legislation:
- Schedule 22 of the Environmental Permitting Regulations: the proposals
do not include requisite surveillance and monitoring measures.
- Water Act (2003) A hydrogeological impact appraisal has not been
undertaken to ascertain the impacts of dewatering the excavation on the
local water environment.
- Flood and Water Management Act (2010) The proposed surface water
drainage system is insufficient to manage estimated groundwater
discharge volumes, and sustainable drainage is unlikely to be achieved.
- Water Framework Directive (2010) The groundwater treatment proposed
prior to discharge of groundwater to surface water drainage is not
considered protective of water quality, and is likely to result in pollution
of surface water bodies.
- Landfill Directive (1999). The risks arising from development of a
saturated waste body in the post operational phase have not been
adequately assessed; the risks arising from basal heave, rupture of the
landfill liner and release of hazardous substances and non-hazardous
pollutants to the aquifer have not been recognised or assessed.
- Schedule 4 of the Town and Country Planning (Environmental Impact